1. Field of the Invention
This invention relates to a transfer device for transferring articles disposed in a linear array on a conveyor transversely of the conveyor into an article processing unit. More particularly, this invention relates to a transfer device of the foregoing character for transferring freshly formed glass containers to the upper horizontal surface of a moving conveyor of an annealing lehr, namely, a type of transfer device often called a lehr loader or a stacker.
2. Description of the Prior Art
U.S. Pat. No. 5,044,488 (Bolin) discloses a lehr loader or stacker having a vertical series of driven carriages, the lowermost of which is supported by a support structure at an elevation above the floor of the plant in which the lehr loader is installed. The lowermost carriage is movable toward an adjacent annealing lehr to advance a linear series of glass containers on a conveyor, described in the reference as a cross-conveyor, positioned between the stacker and the lehr, transversely of the cross-conveyor into the lehr. An intermediate carriage is mounted on the lowermost carriage. The intermediate carriage is movable with the lowermost carriage toward and away from the lehr and is independently movable with respect to the lowermost carriage in a direction parallel to the direction of movement of the cross-conveyor to keep new containers on the cross-conveyor from piling up against a pusher bar carried by a third carriage during the motion of the lowermost carriage toward the lehr. The third carriage, which is the uppermost carriage in the series, is mounted above the intermediate carriage and is movable with the lowermost carriage and the intermediate carriage and is movable in a vertical direction independently of the intermediate carriage and the lowermost carriage to elevate the pusher bar above the tops of incoming containers on the cross-conveyor during the return of the pusher bar to a start position. The motion of each of the carriages of the stacker of the aforesaid U.S. Pat. No. 5,044,488 is actuated by an axially fixed, rotatable screw drive carried by the underlying carriage, or the support structure in the case of drive for the lowermost carriage, and the rotatable screw is rotatable in a nut that is fixed to the drive carriage.
The rotating screw carriage drives of a stacker according to the aforesaid U.S. Pat. No. 5,044,488 have many operating advantages over other lehr loader carriage drive techniques, such as hydraulic or pneumatic cylinders or motors, in that rotating screw drives have higher starting torques and are less jerky and more controllable in their motions. Unfortunately, the environment of a glass container manufacturing facility is quite hostile to rotating screw drives of the type described in the aforesaid U.S. Pat. No. 5,044,488, due to dust or other particles that may contaminate the nut contacting surfaces of the rotatable screws, or the tendency of the rotatable screws to sling lubricant outwardly when rotating at the speeds of rotation needed for proper operation of a lehr loader, and/or the high temperatures that are inherently present in the operation of a lehr loader. Because of such problems, the inventor of the aforesaid U.S. Pat. No. 5,044,488 subsequently patented a lehr loader that substituted endless belt drives for the rotatable screw drives of the aforesaid U.S. Pat. No. 5,044,488, as is shown in U.S. Pat. No. 5,472,077 (Bolin). However, the use of endless drives to drive the carriages of a lehr loader introduces other problems into the operation of a lehr loader, such as the inherent low starting torque of such drives and problems encountered in accurately controlling the positions of the movable carriages due to the stretching of belts in a belt-driven system or the backlash between chains and drive sprockets in a chain-driven system.
Other lehr loaders are disclosed in U.S. Pat. Nos. 4,067,434 (Mumford) and 3,184,031 (Dunlap), which were assigned to the assignee of this application or one of its predecessors, the disclosure of each of which is incorporated by reference herein, and in published UK Patent application GB 2174667A.